Three types of substances in water contribute to blocking the light. All of them can trace their origins back to land:
1. suspended particulate matter : soils or other suspended sediments in the water.
2. phytoplankton : microscopic algae that feed on nutrients, like phosphorus and nitrogen, that stream off the land.
3. colored dissolved organic matter (CDOM) : decaying plant material, or “yellow substances.” CDOM acts like a tea bag, staining the water yellow or brown by releasing tannins.